1. Field of the Invention
The present invention relates to a patch antenna and a wireless device, and more particularly to a patch antenna which has degenerate separation elements thereof and switches between the degenerate separation elements according to a polarized wave, and a wireless device which has the above patch antenna.
2. Description of the Related Art
In these years, cell phones (or mobile phone) have been increasing in functional versatility, and have been equipped with various applications using radio. An example of such cell phones is a cell phone having the function of identifying its location using the GPS (Global Positioning System). This cell phone has a circularly polarized wave patch antenna for reception of GPS radio waves (a circularly polarized wave patch antenna for the GPS) to receive a radio wave from a GPS satellite.
It is desirable for a circularly polarized wave patch antenna to efficiently receive a circularly polarized wave regardless of whether it is left-hand circular polarization (LHCP) or right-hand circular polarization (RHCP). For this purpose, a patch antenna is proposed which is arranged on six faces of a cube-shaped solid, thereby, without switching of a receivable polarized wave, preventing the presence of a plane on which a receivable polarized wave switches from one to another (see Japanese Patent Laid-Open No. 2001-332929). A patch antenna is also proposed which is allowed to easily deal with left-hand circular polarization and right-hand circular polarization by providing a dielectric for adjustment on a feeding patch (see Japanese Patent Laid-Open No. 2003-347832). Further, various shapes are proposed as candidates for the shape of a patch element (see Japanese Patent Laid-Open No. 5-167335).
In a cell phone, a circularly polarized wave patch antenna is optimized only for one of open and shut (or closed) states of a housing, and is not optimized for the other. That is, the cell phone cannot control a circularly polarized wave according to the open/shut state of the housing. Accordingly, the cell phone suffers a large loss and inefficiency for receiving weak radio waves.
Since a radio wave from a GPS satellite is RHCP, for example, assume that a flip cell phone is designed to efficiently receive such a polarized wave in an open state (a state in which a movable unit having a liquid crystal display is opened). In this case, a polarization direction as viewed from an antenna is a direction of right-hand rotation. That is, this circularly polarized wave patch antenna for the GPS is an antenna for RHCP reception. On the other hand, in a shut state (a state in which the movable unit is shut or closed), a radio wave from the GPS satellite is received from on the reverse side of the antenna. In this case, the polarization direction as viewed from the antenna is a direction of left-hand rotation, and the reception is equal to reception of a LHCP radio wave by the antenna for RHCP reception. That is, cross polarization occurs, and the antenna characteristics appear to be deteriorated.
Under the circumstances, there is a need for an antenna capable of switching a polarized wave to be received according to the open/shut state of a housing of a cell phone, regardless of the open/shut state of the housing. However, a patch antenna to be mounted in a small terminal such as a cell phone needs to be small. For example, it is very difficult to mount a cube-shaped patch antenna described in Japanese Patent Laid-Open No. 2001-332929 in a terminal such as a cell phone.